Waste to energy ash and engineered aggregate in road construction

ABSTRACT

Described herein are compositions and methods for waste-to-energy ash in engineered aggregate in road construction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. utility application Ser. No.15/631,743, filed Jun. 23, 2017, which claims priority to U.S.provisional application Ser. No. 62/353,732, filed on Jun. 23, 2016,both of which are incorporated herein by reference in their entireties.

BACKGROUND

Waste-to-energy (WTE) is a form of energy recovery that can generateenergy, such as heat or electricity, from the primary treatment ofwaste. Incineration is a primary treatment used frequently in WTEschemes that generates ash byproducts (fly ash and bottom ash) duringwaste incineration and energy generation. There is currently interest insystems and methods directed at the reuse recycling of WTE ash insteadof landfill disposal. The use of WTE bottom ash (BA) as a roadway basecourse or as an aggregate replacement in hot mix asphalt (HMA) orPortland cement concrete (PCC) pavements are potential applications forWTE BA recycling. While WTE BA displays potential for theseapplications, problems such as hydrogen gas generation and heavy metalleaching preclude the widespread use of WTE BA in road construction. Thepresent disclosure discusses compositions and methods forwaste-to-energy ash in engineered aggregate in road construction, toaddress the aforementioned deficiencies and inadequacies.

SUMMARY

Described herein are compositions of waste-to-energy bottom ash. Inembodiments, compositions comprising waste-to-energy bottom ash (WTE BA)aggregates sized about 9.5 mm to about 19.05 mm, wherein the compositionhas an aluminum content of about 25,000 mg/kg dry or less. The aluminumcontent can be determined using EPA testing method 3050b.

Compositions as described herein can comprises about 12% to about 20% oftotal WTE BA that passes through a ⅜ inch sieve.

Compositions as described herein can comprise WTE BA aggregates andwater, which form an aqueous suspension with a pH of about 11 or lessbasic.

Compositions as described herein can react with CO₂ from a CO₂ source.

Compositions as described herein can be Portland cement concretecompositions comprising Portland cement concrete and a WTE BA aggregatefraction, wherein the WTE BA aggregate fraction contains WTE BAaggregates of about 9.5 mm to about 19.05 mm in size, wherein theaggregate fraction has an aluminum content of about 25,000 mg/kg dry orless. Aluminum content of compositions such as these can be determinedusing EPA testing method 3050b. In compositions such as these, the WTEBA aggregate fraction can be about 50% or less of the total composition.Compositions can further comprise coal fly ash. Portland cement concretecompositions can comprise a WTE BA aggregate fraction that has beenmixed with water to form an aqueous suspension with a pH of about 8 toabout 11. The WTE BA aggregate fraction of PCC compositions can bereacted with CO₂ from a CO₂ source.

Described herein are compositions of hot mix asphalt (HMA), comprisinghot mix asphalt and a WTE BA aggregate fraction, wherein the WTE BAaggregate fraction contains WTE BA aggregates between about 9.5 mm toabout 19.05 mm in size, wherein the aggregate fraction has an aluminumcontent of about 25,000 mg/kg dry or less. The aluminum content can bedetermined using EPA testing method 3050b. The WTE BA aggregate fractioncan be about 50% or less of the total composition. The WTE BA aggregatefraction can be mixed with water to form an aqueous suspension with a pHof about 11 or less basic. HMA compositions as described herein canfurther comprise coal fly ash. The WTE BA aggregate fraction of HMAcompositions can be reacted with CO₂ from a CO₂ source.

Described herein are methods of altering a composition ofwaste-to-energy bottom ash (WTE BA), comprising separating WTE BA with afirst separation device to isolate a first WTE BA aggregate fraction,wherein the first aggregate fraction contains WTE BA aggregates about9.5 mm or larger in size; and separating the first WTE BA aggregatefraction with a second separation device to isolate a second aggregatefraction, wherein the second aggregate fraction contains WTE BAaggregates of about 9.5 mm to about 19.05 mm in size, wherein the secondaggregate fraction has an aluminum content of about 25,000 mg/kg dry orless. The aluminum content can be determined using EPA method 3050b. Thefirst separation device can be a ⅜ inch sieve. The second separationdevice can be a ¾ inch sieve. Methods as described herein can furthercomprise reacting the second aggregate fraction with CO₂ from a CO₂source. Methods as described herein can further comprising aging thesecond aggregate fraction after separating the first WTE BA aggregatefraction, wherein aging the second aggregate fraction comprises placingthe second aggregate fraction in a lined unit, adding water to thesecond aggregate fraction to form an aqueous suspension, and reactingthe aqueous suspension with CO₂ from a CO₂ source over a period of timeuntil the pH of the second aggregate in aqueous suspension is betweenabout 8.0 to about 11.0.

Portland cement concrete compositions as described herein can comprisetricalcium silicate, dicalcium silicate, tricalcium aluminate,tetracalcium aluminoferrite, free calcium oxide, and sulfur trioxide,individually or in combination.

Hot mix asphalt compositions as described herein can comprise sand, RAP,course aggregate, and screenings, individually or in combination.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the disclosed devices and methods can be betterunderstood with reference to the following drawings. The components inthe drawings are not necessarily to scale, emphasis instead being placedupon clearly illustrating the relevant principles.

Moreover, in the drawings, like reference numerals designatecorresponding parts throughout the several views.

FIGS. 1(a)-(c) illustrate ash characterization data.

FIG. 2 represents an embodiment of a lined unit.

FIG. 3 shows aluminum (Al) cumulative mass release in method 1315.

FIG. 4 depicts a log-log comparison of the cumulative release of Al(mg/m²) and leaching.

FIG. 5 illustrates log-log comparison of the cumulative release ofmolybdenum (Mo) from concrete pavements (mg/m²) and leaching accordingto method 1315.

FIG. 6 shows leached synthetic precipitation leaching procedure (SPLP)concentrations for embodiments of ash amended and control pavements.

FIG. 7 represents the total environmentally available concentration oftrace elements in embodiments of ash amended and control pavements.

FIG. 8 illustrates method 1315 constituents of potential concern (COPC)release and eluate pH from embodiments of concrete pavements.

FIG. 9 illustrates method 1315 COPC release and eluate pH fromembodiments of asphalt pavements.

FIG. 10 shows leachability index and observed diffusivity.

FIG. 11 shows grain size distribution of WTE bottom ash (WTE BA) used inembodiments of pavement samples.

FIG. 12 depicts an example of roadway construction.

FIG. 13 depicts an example of asphalt roadway construction.

FIG. 14 depicts embodiments of mix design of ash-amended pavements.

FIGS. 15(a) and (b) depict embodiments of asphalt mix design andvolumetric properties used for ash-amended pavement[s] (a) and mixproperties (b).

FIG. 16 shows pavement dry density and exposed surface area ofembodiments of concrete and asphalt pavements.

FIG. 17 represents a list of leached elements in SPLP test and totalconcentrations of leached concentration of elements in SPLP testaccording to embodiments of the present disclosure.

FIG. 18 shows total environmentally available concentrations of traceelements in ash amended and control pavements according to embodimentsof the present disclosure.

FIG. 19 shows bottom ash aggregate data and laboratory and field mixesof embodiments of the present disclosure.

FIG. 20 shows ash specific gravity, absorption, and results of LosAngeles abrasion testing according to embodiments of the presentdisclosure.

FIG. 21 shows 28 day compressive strength of an embodiment of coarseaggregate replaced with LT-9.5 ash.

FIG. 22 depicts 28 day compressive strength of an embodiment of coarseaggregate replaced with GT-9.5 ash.

FIG. 23 shows carbonated ash-amended concrete compressive strength of anembodiment using GT-9.5 ash.

FIG. 24 illustrates uncarbonated ash-amended concrete compressivestrength of an embodiment using GT-9.5 ash.

FIG. 25 shows carbonated ash-amended concrete dry length change of anembodiment of concrete using GT-9.5 ash.

FIG. 26 shows uncarbonated ash-amended concrete dry length change of anembodiment of concrete using GT-9.5 ash.

FIG. 27 shows uncarbonated ash concrete resistivity according to anembodiment of the present disclosure.

FIG. 28 shows carbonated ash concrete resistivity according to anembodiment of the present disclosure.

FIG. 29 depicts grain size distribution of LT-9.5 and GT-9.5 ash.

FIG. 30 shows mass percentage passing of ash through different sizedsieves.

DETAILED DESCRIPTION

Before the present disclosure is described in greater detail, it is tobe understood that this disclosure is not limited to particularembodiments described, as such may, of course, vary. It is also to beunderstood that the terminology used herein is for the purpose ofdescribing particular embodiments only, and is not intended to belimiting, since the scope of the present disclosure will be limited onlyby the appended claims.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit (unlessthe context clearly dictates otherwise), between the upper and lowerlimit of that range, and any other stated or intervening value in thatstated range, is encompassed within the disclosure. The upper and lowerlimits of these smaller ranges may independently be included in thesmaller ranges and are also encompassed within the disclosure, subjectto any specifically excluded limit in the stated range. Where the statedrange includes one or both of the limits, ranges excluding either orboth of those included limits are also included in the disclosure.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this disclosure belongs. Although any methods andmaterials similar or equivalent to those described herein can also beused in the practice or testing of the present disclosure, the preferredmethods and materials are now described.

As will be apparent to those of skill in the art upon reading thisdisclosure, each of the individual embodiments described and illustratedherein has discrete components and features which may be readilyseparated from or combined with the features of any of the other severalembodiments without departing from the scope or spirit of the presentdisclosure. Any recited method can be carried out in the order of eventsrecited or in any other order that is logically possible.

Embodiments of the present disclosure will employ, unless otherwiseindicated, techniques of chemistry, inorganic chemistry, materialscience, and the like, which are within the skill of the art. Suchtechniques are explained fully in the literature.

The following examples are put forth so as to provide those of ordinaryskill in the art with a complete disclosure and description of how toperform the methods and use the compositions and compounds disclosed andclaimed herein. Efforts have been made to ensure accuracy with respectto numbers (e.g., amounts, temperature, etc.), but some errors anddeviations should be accounted for. Unless indicated otherwise, partsare parts by weight, temperature is in ° C., and pressure is inatmosphere. Standard temperature and pressure are defined as 25° C. and1 atmosphere.

Before the embodiments of the present disclosure are described indetail, it is to be understood that, unless otherwise indicated, thepresent disclosure is not limited to particular materials, reagents,reaction materials, manufacturing processes, or the like, as such canvary. It is also to be understood that the terminology used herein isfor purposes of describing particular embodiments only, and is notintended to be limiting. It is also possible in the present disclosurethat steps can be executed in different sequence where this is logicallypossible.

It must be noted that, as used in the specification and the appendedclaims, the singular forms “a,” “an,” and “the” include plural referentsunless the context clearly dictates otherwise. Thus, for example,reference to “a support” includes a plurality of supports. In thisspecification and in the claims that follow, reference will be made to anumber of terms that shall be defined to have the following meaningsunless a contrary intention is apparent.

DISCUSSION

Embodiments of the present disclosure provide for compositions andmethods for waste-to-energy bottom ash an engineered aggregate in roadconstruction. Incineration is one method of waste-to-energy (WTE)generation that results in ash byproducts, primarily fly coal ash andbottom ash (BA). It can be possible to recycle and reuse WTE ashby-products, BA especially. A potential application for WTE BA recyclingis the use of WTE BA in road construction. Portland Cement Concrete(PCC) and hot mix asphalt (HMA) compositions can be formulated with WTEBA and can be used to construct roads. WTE BA aggregates can also beused as a granular aggregate base course. While there are numerousapplications for the use of recycled WTE BA, the use of WTE BA isproblematic currently in road construction because of environmentalconcerns and concerns relating to the strength of the finished concreteand/or road product.

Described herein are compositions of WTE BA and methods that can alterthe composition of WTE BA aggregates and make WTE BA aggregates moresuitable for use in road construction and materials related to roadconstruction.

Size and composition of WTE BA aggregates can be a factor relating tothe suitability of recycled WTE BA in road construction. Total WTE BAcan be separated with one or more separation devices as described hereinto create a composition or alter the composition of WTE BA and producespecific WTE BA gradations, aggregate fractions, and/or separated WTE BAaggregates of a desired size. As used herein, compositions of WTE BA canbe WTE BA aggregates that constitute an aggregate fraction, and acomposition of WTE BA can be a WTE BA aggregate fraction comprised ofWTE BA aggregates. The one or more separation devices can be sieves, andcan comprise a ⅜ inch sieve and/or a ¾ inch sieve. As used herein, ⅜ ofan inch can be about 9.5 mm and ¾ of an inch can be about 19.05 mm.Alternatively, 9.5 mm can be about ⅜ of an inch and 19.05 mm can beabout ¾ of an inch.

In an embodiment, WTE BA can be separated with one or more separationdevices, which can be sieves, and can comprise a ⅜ inch sieve and/or ¾inch sieve, until aggregates and/or an aggregate fraction of a desiredsize are produced. In an embodiment, WTE BA can be separated untilseparated WTE BA aggregates having a size of about ⅜ of an inch to about¾ of an inch are the only aggregates remaining. In an embodiment, WTE BAcan be separated until separated WTE BA aggregates having a size ofabout ½ of an inch to about ⅝ of an inch are the only aggregatesremaining. The size of the aggregates as used herein can be the radius,diameter, circumference, length, width, area, volume, cross-sectionalsurface area, or other physical dimension of a WTE BA aggregate. Afterseparation with one or more separation devices, separated WTE BAaggregates having a size of about ¾ inch to about ⅜ inch can be usedaccording to the systems and methods described herein. Separated WTE BAaggregates for use according to the systems and methods described hereincan be within a WTE BA aggregate fraction that represents about 12% toabout 30%, or about 15% to about 30%, or about 15% of total WTE BA thatpasses through a ⅜ inch sieve. WTE BA aggregates can be with a WTE BAaggregate fraction that represents about 12% to about 25%, about 15% toabout 25%, or about 20% of total WTE BA that passes through a ¼″ sieve.

In an embodiment, a separation device can be used to first remove WTE BAaggregates and/or particulates smaller than about 9.5 mm, producing aWTE BA aggregate fraction. The WTE BA aggregate fraction can besubjected to a second separation device wherein WTE BA aggregates and/orparticulates of about 19.05 mm or larger are removed from the aggregatefraction. In another embodiment, WTE BA can be subjected to a firstseparation device where WTE BA aggregates and/or particulates of about19.05 mm or larger are removed, producing an aggregate fraction, andthen the aggregate fraction subjected to a second separation device thatremoves WTE BA aggregates and/or particulates of about 9.5 mm or less.In an embodiment, a WTE BA aggregate fraction contains WTE BA aggregatesranging in size of about 9.5 mm to about 19.05 mm or about ⅜ of an inchto about ¾ of an inch. Alternatively, a separation device can becomprised of one or more grates that separate out and/or isolate a WTEBA aggregate fraction containing WTE BA aggregates sized about 9.5 toabout 19.05 mm for use in road construction. In an embodiment, a trommelscreen can be a separation device used to separate out and/or isolate aWTE BA aggregate fraction containing WTE BA aggregates sized about 9.5to about 19.05 mm. Separation devices as described herein can optionallybe vibrated or coupled to a vibration device or device that vibrates theone or more separation devices to aid in size-separation of WTE BAaggregates. The systems and methods of WTE BA separation as describedherein can alter the composition of WTE BA and remove elements, alloys,particulates, and/or other contaminants from the WTE BA that aredetrimental to the use of WTE BA in road construction. One or moreseparation devices as described above can be used to change the sizeand/or composition of WTE aggregates and can remove metals, elements,alloys, and/or other contaminants from the WTE BA. Examples of metalsand elements that can be removed from WTE BA aggregates and/or a WTE BAaggregate fraction are aluminum (Al), arsenic (As), boron (B), barium(Ba), calcium (Ca), cadmium (Cd), cobalt (Co), iron (Fe), potassium (K),magnesium (Mg), sodium (Na), antimony (Sb), strontium (Sr), zinc (Zn),alloys of any combination of these, or others. The one or moreseparation devices can alter the composition of WTE BA aggregates andproduce WTE BA aggregates that generate less hydrogen (H₂) gas whenincorporated into road construction materials than naïve, unseparatedand/or unaltered WTE BA aggregates, which is advantageous because it canincrease the structural integrity and/or strength of resulting roadproducts.

Environmental Protection Agency (EPA) testing method 3050b (aciddigestion of sediment, sludge, and soil) is one method that can be usedto determine composition of WTE BA aggregates and/or aggregatefractions. Other tests that can be used to determine composition(elemental, alloy, contaminant, and/or otherwise) of WTE BA aggregatesand/or aggregate fractions can include acid digestion with nitric and/orhydrofluoric acid (EPA Method 3052 for example), x-ray fluorescence, andreaction with hydroxides (OH—). Tests using reaction with hydroxides canevaluate composition (such as Al content) through the volumetricmeasurement of hydrogen gas produced by the reaction of the element,alloy, or contaminant (which can be Al or contain Al) in WTE BAaggregates and/or aggregate fractions. Exact measurements produced bydifferent tests may produce different results as some testingmethodology is destructive (and destroys some of the components to bemeasured, producing lower measurements than non-destructive methods) andsome testing methods are non-destructive.

In an embodiment, a WTE BA aggregate fraction contains a total Alcontent of about 5,200 mg/kg (dry) to about 14,200 mg/kg (dry). In anembodiment, a WTE BA aggregate fraction contains a total Al content ofabout 9,670 mg/kg (dry). In an embodiment, a WTE BA aggregate fractioncontains a total Al content of less than about 25,000 mg/kg (dry). In anembodiment, a WTE BA aggregate fraction contains a total Al content ofless than about 14,200 mg/kg (dry). In an example, a WTE BA aggregatefraction contains a total Al content of less than about 25,000 mg/kg(dry) as determined by EPA testing method 3050b.

In an embodiment, a WTE BA aggregate fraction contains WTE BA aggregatessized about 9.5 mm to about 19.05 mm, and the WTE BA aggregate fractionhas a total Al content of about 9,670 mg/kg (dry) or less. In anembodiment, a WTE BA aggregate fraction contains WTE BA aggregates sizedabout 9.5 mm to about 19.05 mm, and the WTE BA aggregate fraction has atotal Al content of about 25,000 mg/kg (dry) or less. In an example, aWTE BA aggregate fraction contains WTE BA aggregates sized about 9.5 mmto about 19.05 mm and the aggregate fraction has a total Al content ofless than about 25,000 mg/kg (dry) according to EPA testing method3050b.

In an embodiment, a WTE BA aggregate fraction contains WTE BA aggregatessized about 9.5 mm to about 19.05 mm, and the WTE BA aggregate fractionhas a total Al content of less than about 25,000 mg/kg (dry). In anembodiment, a WTE BA aggregate fraction contains WTE BA aggregates sizedabout 4/8 of an inch to about ⅝ of an inch, and the WTE BA aggregatefraction has a total Al content of less than about 25,000 mg/kg (dry).In an embodiment, a WTE BA aggregate fraction contains WTE BA aggregatessized about 9.5 mm to about 19.05 mm, and the WTE BA aggregate fractionhas a total Al content of less than about 14,200 mg/kg (dry). In anembodiment, a WTE BA aggregate fraction contains WTE BA aggregates sizedabout 9.5 mm to about 19.05 mm, and the WTE BA aggregate fraction has atotal Al content between about 5,200 mg/kg (dry) and about 14,200 mg/kg(dry). In an embodiment, elements contained in WTE BA and a WTE BAaggregate fraction containing aggregates ⅜″ to ¾″ in size can be seen inFIG. 1(a). Further characterization data can be seen in FIG. 1(b) andFIG. 1(c). In an embodiment, a WTE BA aggregate fraction can: containWTE BA ash aggregates sized about 9.5 mm and about 19.05 mm; have atotal Al content of less than about 14,200 mg/kg (dry); and/or have adry bulk specific gravity of about 2.1 to about 2.5, a saturated surfacedry specific gravity of about 2.2 to about 2.6, an apparent specificgravity of about 2.3 to about 2.7, and an absorption of about 2.0% toabout 5.0%.

Following separation with the one or more separation devices, WTE BAaggregates or a WTE BA aggregate fraction can be optionally be placed ina lined unit for curing and aging. The unit can be of any material ofsuitable strength to retain and/or hold an aqueous mixture containingash. The lining of the unit can be any suitable material that does notpermit the passage of water and/or liquid between an aqueous suspensionin the lined unit and the unit itself. The lining can be a hydrophobicmaterial and can be a material that does not absorb water or otherliquids. The lining of the unit can be constructed of plastic or aplastic-like polymer. The lined unit can be designed to collect and/orretain rainwater or other moisture from the atmosphere. The lined unitcan be constructed and/or configured to receive water from a watersource. The lined unit can be constructed and/or configured to receivecarbon dioxide (CO₂) from a carbon dioxide source (CO₂ source). Anexample of a lined unit is shown in FIG. 2 .

Once in the lined unit, WTE BA aggregates or aggregate fraction canoptionally be mixed with water to form an aqueous suspension. The watercan be rainwater that is collected in the lined unit, or can be anothertype of water from a water source that is delivered into the lined unit,such as water from a well or a reservoir.

Over a period of time, the pH of the aqueous suspension, which cangenerally be alkaline, can decrease and the WTE BA aggregates and/oraggregate fraction cures. The pH of the aqueous suspension can bemeasured by a pH measuring device. The pH measuring device can be any pHmeasuring device known in the art, such as litmus paper or acommercially available pH meter. WTE BA aggregates or aggregate fractionin an aqueous solution with a pH of about 10.5, or about pH 8.0 to aboutpH 11.0, can be suitable for use in PCC and HMA. WTE BA aggregates oraggregate fraction in an aqueous solution with a pH of about 10.5 toabout 9.5 can be suitable for use in PCC and HMA. WTE BA can be left inthe lined unit in the presence of water until the pH of the aqueoussolution is about 11.0 or about 10.5 or less basic.

As the WTE BA aggregate and/or aggregate fraction in the aqueoussolution cures, regions of low solubility within the aggregate and/oraggregate fraction can be created for heavy metals (such as Sb, Al, andPb) contained within the aggregates and/or aggregate fraction. Water inor added to the aqueous suspension can also create a washing effect anddecrease the concentration of other contaminants (such as molybdenum, Moand chloride, Cl⁻) in the WTE BA. It may be possible to base theendpoint for curing WTE BA in an aqueous suspension as herein describedby changes in concentrations of the heavy metals and contaminants in theWTE BA aggregates or aggregate fraction or the aqueous suspension.

WTE BA aggregates can be reacted with carbon dioxide (CO₂) so that theWTE aggregate fraction or WTE BA aggregates within an aggregate fractionare carbonated. Carbonation of the aggregates can reduce hydrogen gasformation or other detrimental effects of the WTE BA aggregates inmaterials related to road construction.

A WTE BA aggregate fraction as described herein can be used in roadconstruction as a part of granular base course. In an example, a WTE BAaggregate fraction used as a partial aggregate replacement in granularbase course has a total Al content of about 25,000 mg/kg (dry) or lessand the WTE BA aggregate fraction contains WTE BA aggregates sized fromabout 9.5 mm to about 19.05 mm. In an embodiment, a WTE BA aggregatefraction as described above or otherwise herein is aged in a lined unitwith water as an aqueous solution until the pH of the aqueous solutionis about 10.5 or about pH 8.0 to about pH 11.0, and then is used as agranular base course. In an embodiment, a WTE BA aggregate fraction asdescribed above or otherwise herein is reacted with CO₂ from a CO₂source and then used as a granular base course.

WTE BA aggregates can be mixed with tricalcium silicate, dicalciumsilicate, tricalcium aluminate, tetracalcium aluminoferrite, freecalcium oxide, sulfur trioxide, and/or gypsum to form a PCC mixture. Inan example, WTE BA aggregates or WTE BA aggregate fractions as describedherein can be mixed with cement type I/II, lime rock, sand, and water toform a PCC mixture. In an embodiment, the PCC mixture as previouslydescribed can be admixed with coal fly ash. In an embodiment, coal flyash is admixed with the PCC mixture at about 2% to about 4% or about2.63% of the total PCC mixture by weight. FIG. 14 shows an embodiment ofa PCC mixture according to the present disclosure. In an example, WTE BAaggregates or WTE BA aggregate fractions as described herein can bemixed with cement type I/II, crushed stone, sand, and water to form aPCC mixture. In an example, WTE BA aggregates or WTE BA aggregatefractions as described herein can be mixed with cement type I/II,gravel, sand, and water to form a PCC mixture. In an example, WTE BAaggregates or WTE BA aggregate fractions as described herein can bemixed with cement type I/II, recycled concrete aggregate, sand, andwater to form a PCC mixture. In an embodiment, silica fume is admixedwith the PCC mixture at about 0.5% to about 1.5% or about 0.8% of thetotal PCC mixture by weight.

WTE BA aggregates can be mixed with RAP, course aggregate, screenings,and sand to form a HMA mixture. Examples of asphalt mixes and mixproperties according to the present disclosure can be seen in FIGS.15(a) and 15(b). WTE BA aggregates can be mixed with course aggregate,screenings, and sand to form a HMA mixture. WTE BA aggregates can bemixed with recycled asphalt pavement (RAP), gravel, screenings, and sandto form a HMA mixture. WTE BA aggregates can be mixed with RAP, crushedstone, screenings, and sand to form a HMA mixture. WTE BA aggregates canbe mixed with RAP, lime rock, screenings, and sand to form a HMAmixture. WTE BA aggregates can be mixed with RAP, lime rock, and sand toform a HMA mixture. WTE BA aggregates can be mixed with RAP, gravel, andsand to form a HMA mixture. WTE BA aggregates can be mixed with RAP,crushed stone, and sand to form a HMA mixture.

In embodiments, PCC or HMA mixtures can be formed with a WTE BAaggregate fraction having a total Al content about 25,000 mg/kg (dry) orless, and the WTE BA aggregate fraction contains WTE BA aggregates sizedbetween about 9.5 mm to about 19.05 mm. PCC or HMA mixtures can beformed according to the embodiments above, where the WTE BA aggregatefraction is also optionally aged in a lined unit in an aqueoussuspension until the aqueous suspension has a pH of about 11 or lessbasic. PCC or HMA mixtures can be formed according to the embodimentsabove, wherein the WTE BA aggregate fraction is also reacted with CO₂from a CO₂ source. A CO₂ source as described herein can be theatmosphere.

PCC or HMA can include a WTE BA aggregate fraction as described hereinat about 50% or less of the total mixture. A WTE BA aggregate fractioncan be about 0.001% to about 50% of the total mixture in PCC or HMA. AWTE BA aggregate fraction can be about 5% to about 45% of the totalmixture in PCC or HMA. A WTE BA aggregate fraction can be about 10% toabout 40% of the total mixture in PCC or HMA. A WTE BA aggregatefraction can be about 15% to about 35% of the total mixture in PCC andHMA. A WTE BA aggregate fraction can be about 20% to about 30% of thetotal mixture in PCC or HMA. A WTE BA aggregate fraction can be about25% of the total mixture in PCC or HMA.

Optionally, a WTE BA aggregate fraction as described herein can beadmixed with coal fly ash in compositions for road construction, such asPCC and/or HMA, and the WTE BA aggregate fraction admixed with coal flyash can be non-aged or aged, and optionally reacted with CO₂. Coal flyash admixed with WTE BA for PCC or HMA can have the followingspecifications: a total mineral composition of SiO₂, Al₂O₃, and Fe₂O₃greater than 70% by mass, maximum SO₃ content of 4.0% (by mass), maximummoisture content of 3%, and maximum loss on ignition of 6%. Inaccordance with ASTM C618 the physical requirements for Class F coal flyash include: <34% of the material retained on a 45 um (No. 325) sievewhen wet-sieved (with a variation of less than 5% points from average).A strength activity index (done in accordance with ASTM C311) of 75% orgreater when compared to the control cements at 7 and 28 days, and awater requirement of less than 105% of the control.

Also described herein is a method for altering the elemental compositionof WTE BA. The method can be comprised of the steps of separating WTE BAwith one or more separation devices. In an embodiment, WTE BA can beseparated with a separation device that removes WTE BA aggregates and/orparticulates smaller than about 9.5 mm to produce an aggregate fraction.The separation device can be a ⅜ inch sieve. The aggregate fraction canthen be separated with a second separation device to remove WTE BAaggregates and/or particulates about 19.05 mm in seize or greater. WTEBA separation can reduce to the total Al content of the resulting WTE BAaggregate fraction to less than 25,000 mg/kg (dry) or less than 14,200mg/kg (dry). In another embodiment, the order of the separation stepsare be reversed.

In an embodiment, the aggregate fraction that remains after separationcan be reacted with CO₂ from a CO₂ source to further alter thecomposition. The CO₂ source can be the atmosphere. In anotherembodiment, the aggregate fraction that remains after separation can beaged to further alter the composition by placing the aggregate fractionin a lined unit and mixing the aggregate fraction with water to form anaqueous suspension. The WTE BA aggregate fraction can remain in theaqueous mixture in the lined unit until the pH of the aqueous suspensionis about 10.5 or about pH 7.0 to about pH 11.0.

The resulting WTE BA aggregate fraction can then be used in roadconstruction, either as a granular base course or in PCC or HMA or othermaterials as described herein, with or without the optional CO₂ reactionsteps or aging steps.

EXAMPLES

Now having described the embodiments of the disclosure, in general, theexamples describe some additional embodiments. While embodiments of thepresent disclosure are described in connection with the example and thecorresponding text and figures, there is no intent to limit embodimentsof the disclosure to these descriptions. On the contrary, the intent isto cover all alternatives, modifications, and equivalents includedwithin the spirit and scope of embodiments of the present disclosure.

Example 1

1.0 Introduction

It is well known that waste-to-energy (WTE) bottom ash (BA) represents apotential material for inclusion into the circular economy and that thisresource is underutilized in many parts of the world [1]. Many uses forWTE BA have focused on reuse as a component in roadway constructionprojects including: the use of WTE BA as a roadway base course [1-4] oras an aggregate replacement in hot mix asphalt (HMA) or Portland cementconcrete (PCC) pavements [5-10]. The use of recycled WTE BA as a roadbase course can result in the release of relatively small amounts ofcertain trace elements into the environment [2, 3, 11]. Additionally,because heavy metals are enriched in the ash during the combustionprocesses, total concentrations of certain trace elements have beenfound to exceed risk-based concentration thresholds for direct humanexposure (depending on the thresholds used) [1, 12, 13].

One avenue to mitigate some of the potential concerns (leaching anddirect human exposure risks) related to the beneficial use of WTE BA inroadway construction projects is to encapsulate the material inside anasphaltic or concrete matrix. Encapsulation of WTE BA and other similarcombustion residues has been demonstrated to decrease contaminantleaching into the environment [6, 8, 14, 15] and to reduce direct humanexposure risk by minimizing the opportunity for contact. Research hasillustrated that the use of WTE BA as a partial aggregate replacement inHMA [7, 8, 14, 16-21] and PCC [5, 6, 9, 10, 22] is feasible. However,studies have pointed to possible deleterious effects when the materialis added in high replacement quantities (> approximately 30%). Theseeffects include an increase in binder content when the material is addedto HMA [8, 17, 18] and hydrogen gas generation, resulting in spallingand decreased compressive strength, when added to PCC [9, 10, 22].

The risk of contamination to water supplies from a waste material istypically assessed using a leaching test. Batch leaching tests provideessential information on contaminant release from size-reduced wastematerials, but are often considered a conservative estimate of traceelement leaching from a waste placed as part of a large,semi-impermeable monolith (such as a pavement) [23, 24]. Test methodshave been developed to better assess element release from wastematerials in these forms [23, 25]; these tests allow for the measurementof the time dependent release of elements and the calculation ofobserved elemental diffusivity [23, 25]. Monolithic leaching tests havebeen used by a number researches to evaluate trace element mobility fromwaste materials that have been encapsulated with asphalt or cement [15,26-30].

In an effort to further the body of scientific knowledge related to WTEash reuse, a pilot project was conducted for a municipality in Floridaduring the summer of 2014. This project involved the construction of aseries of roadway test strips, two of which incorporated WTE BA as apartial aggregate replacement in pavements (one in HMA and one in PCC).Control tests strips were constructed using the same mix designs exceptthat virgin construction materials were used for the portion of theaggregate previously replaced with ash. This provided the research teamwith the unique opportunity to sample ash-amended and control pavements(both HMA and PCC) produced at full scale batch plants using the samebase mix design. Additionally, it allowed for the comparison of elementrelease between HMA and PCC. Although comparisons have been made betweenash-amended and control pavements (HMA or PCC) this study represents anovel contribution in comparing the relative degree of encapsulationbetween the two pavement types

Samples of both the control and ash-amended HMA and PCC were takenduring the pilot project; batch and monolithic leaching tests and totalenvironmentally available element composition were conducted. This datawas used to quantify the relative risk posed by these materials whenplaced as a pavement, as well as assess any increased leaching risk thatmight occur when the material was crushed (a common method of recyclingHMA and PCC). A comparison of the element release from the ash-amendedpavements to the pavements constructed with the virgin materials wasperformed to assess whether any of the constituents of potential concern(COPC) were a consequence of the inclusion of the WTE BA into thepavement structure. The leachability index (LI), an indicator of themobility of trace elements from a monolith (in a diffusion controlledscenario), was calculated for the pavements along with the observedelemental diffusivity. The results of this study provide valuableinsight into contaminant release from ash-amended products and are ofsignificance to parties (scientists, municipalities, regulators, andindustry) interested in moving forward with ash reuse in these types ofapplications.

2.0 Materials and Methods

2.1 Facility Description, Sample Collection, and Pavement Design

The ash used in the construction of the pilot scale roadway originatedfrom a 1,000 ton per day, mass burn WTE facility in Florida, US.Following combustion, this facility employs both ferrous and non-ferrousmetals recovery; this is conducted on solely the bottom ash (as opposedto metals recovery being conducted on the mixed ash stream, typical ofmany US WTE facilities). The result of this practice is an increasedpercentage of metals recovery; this is important as it is known that thefraction of metals contained in WTE ash can have a significant impact onits leachability [31].

A grain size distribution of the “as-used” ash, description of the ashprocessing, the HMA and PCC mix designs, and photographs of roadwayconstruction are provided in the supplementary information (SI) sectionavailable following the references. Prior to use, the material was agedfor a period of 2.5 months, representative samples were collected fromthe aging pile for characterization prior to production of the HMA andPCC. The screened BA was used as a 20% replacement of the courseaggregate in the PCC mixture (13% by mass) and 20% of the aggregate inthe HMA mixture (19% by mass). PCC samples were collected from eachtruck in accordance with ASTM C172 [32]. HMA samples were collected bycoring the roadway at three locations (representing the beginning,middle and end of the pavements) approximately one week after placement.

2.2 Total Concentration

The total environmentally available concentration of the elements in thepavements and WTE BA were assessed using EPA method 3050b, fivereplicates of each material (PCC, HMA and BA) were tested. The digestionentails heating the samples at a constant temperature of 95±5° C. whileadding nitric and hydrochloric acids, as well as hydrogen peroxide [33].

2.3 Leaching Tests

EPA method 1312, the synthetic precipitation leaching procedure (SPLP),was conducted on the HMA and PCC pavements as well as the WTE BA. TheSPLP is a batch leaching test conducted at an “as is” liquid to solid(L/S) ratio of 20:1 with samples size reduced to pass a 9.5 mm sieveprior to testing; all SPLP testing was conducted on a homogenized samplerepresenting samples either taken from all of the trucks (PCC) or coresfrom each of the three locations of the roadway (HMA), SPLP tests wereconducted in triplicate.

Determination of mass flux and observed diffusivity from monolithleaching tests is an approach that has been used by a number ofresearches when evaluating COPC release from media where mobility wouldlikely be to be governed by diffusion [e.g., a waste incorporated inconcrete or treated with solidification/stabilization (S/S)] [27,34-36]. A similar approach was included as a part of the US-EPA's newcompendium of leaching tests and was used in this study [25]. EPA method1315 (monolith test), was conducted on the intact HMA and PCC samples.Method 1315 is a tank test where an intact sample is submerged in avessel with reagent water, and the water is renewed at set timeintervals (0.08, 1.0, 2.0, 7.0, 14, 28, 42, 49, and 63 days), all method1315 tests were conducted in triplicate [33]. The samples tested werecylindrical in shape, with a diameter of 10.16 cm and ranged in heightfrom 9.52 to 10.16 cm for the PCC samples and 6.19 to 7.77 cm for theHMA samples. A liquid to exposed surface area ratio (L/SA) of 9±1 mLreagent water per cm² of pavement area was used throughout the method1315 test.

The equations for the calculation of the cumulative mass release, flux,and observed diffusivity from the results of method 1315 can be found inthe SI section. To calculate the observed elemental diffusivity for eachinterval (D_(i) ^(obs)) from the pavement samples, an analyticalsolution derived from Crank (1975) [37] for diffusion from a cylinderinto an infinite bath was used. The leachability index (LI) iscalculated by taking the −1*log₁₀ (D_(i) ^(obs)), where D_(i) ^(obs) isexpressed in units of cm²/s; wastes with a leachability index of <6.5are considered to have high mobility, 6.5<L<8.0 moderate mobility, andL>8.0 limited mobility [28, 36, 38, 39].

2.4 Analytical Methods

Leachate samples were prepared for analysis by conducting an aciddigestion in accordance with EPA Method 3010a [33] (Acid Digestion ofAqueous Samples and Extracts for Total Metals for Analysis by FLAA orICP Spectroscopy). Following the digestion, all samples (leaching testextracts and total digestions) were analyzed for the following inorganicelements: Al, As, B, Ba, Be, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Mo, Na, Ni,Pb, Sb, Se, Sn, Sr, V, and Zn using Inductively Coupled Plasma—AtomicEmission Spectrometry (ICP-AES) (Thermo iCAP 6200 Atomic EmissionSpectrometer).

2.5 Risk Assessment Approach

Often times, as a mechanism of quantifying the relative risk associatedwith the beneficial use of a waste material, leachate concentrations arecompared to regulatory thresholds. In this study, the FloridaGroundwater Cleanup Target Levels (GCTL) were used as the regulatorythreshold for comparison; many of these thresholds are set at the USprimary drinking water standards. The GCTLs were not specificallydeveloped for a beneficial use assessment, but do represent aconservative method for a screening analysis to identify COPC [40].

3.0 Results and Discussion

3.1 Batch Leaching Tests

Al, Mo, and Sb were the three elements which leached above GCTLs in theWTE BA and were identified as COPCs along with Pb, an element known toleach from fresh WTE BA due to its high pH [1]; the mean SPLP pH for theWTE BA was 10.97. Similarly Al, Mo and Sb were found to leach abovetheir respective GCTLs in the SPLP for one or more of the pavementsamples. The results of the SPLP tests are provided in FIG. 6 .

The incorporation of the BA to the PCC did not cause any additionalelements to leach above their respective risk thresholds. Mo, the onlyelement with a health-based risk threshold found to leach above itsGCTL, was present at higher concentrations in the control SPLP leachatesthan in the ash-amended leachates. Pb, an element known to be highlysoluble in BA in the elevated pH range seen (11.5-12.0) [41] did leach;however, the measured concentrations were low, indicating that even whenthe material was size reduced, Pb (and other trace elements present inthe BA) can be bound in the PCC matrix.

The total environmentally available concentrations of select elements(Al, Sb, Pb, Mo) in the pavements are reported in FIG. 7 . The totalconcentrations, along with variations in pH between the PCC and HMA,help to elucidate differences in the SPLP tests.

Mo, found naturally in PCCs and known to be present as an oxyanion [42],was measured at a higher total concentration in the control PCCs(compared to the ash-amended PCCs). A higher concentration could likelyhave resulted in the increased leaching of Mo seen in the controls.Total concentrations of Al were found to be higher in the ash-amendedPCC, as Al is known to be present in BA in significant quantities (asseen in FIG. 7 ) [43]. The speciation of the Al and other elements inthe PCC could drive leaching along with concentration and pH, priorstudy has reported the formation of aluminum carbonate hydrates(Ca₄Al₂O₆(CO₃)_(0.5)·12H₂O; Ca₈Al₄O₁₄·12H₂O) [22] in WTE BA amendedconcrete which could be soluble at the pH values seen here.

Sb and Al can be found in concentrations above their respective GCTLsfor the ash-amended HMA samples. Magee et al. (1999) found that the SPLPpH of ash-amended HMA (10.4) was approximately 0.4 pH points higher thanthat of controls [16]. The data here differed from what was observed inthe previous study; however, a different ash sample was used and thenatural pH of the control HMA (from Magee et al.) was elevated withrespect to the natural pH seen here. In regards to the pH, it may bepossible that the alkalinity of the BA can influence the leachate pH, asthe SPLP of the WTE BA can be higher than the values measured for theHMA samples.

The ash-amended HMA was found to leach Al and Sb in different amountsthan controls. Sb, present in the BA [44], was not detected in thetotals analysis for the control pavements. Differences in Al leachingcould be due to the difference in pH (≈1.5), which can create a morefavorable environment for Al release.

The ash-amended HMA was found to leach in different amounts than theash-amended PCC, even if the differences in ash replacement percentagewere accounted for (HMA-19% PCC-13%, a 6% difference). For Sb, Sbrelease could be more favorable at a lower pH value [45]. The oppositemay be true for Al however, as the pH observed for the PCCs could bemore likely to facilitate Al release [41]. Because of this, it may bepossible that there are other mechanisms which could potentially act toreduce leaching of the ash-amended PCC. The reactivity of BA when placedin PCC has been reported by a number of authors [5, 6, 9, 10], and thesereactions could potentially chemically bind certain trace elements (suchas Pb, which would be suitable to be released at pH of 12) within thePCC matrix. Additionally the permeability of PCC can be several ordersof magnitude lower than that of HMA [46, 47], and therefore reducedleaching of elements due to a slower rate of moment of water within thematerial could be possible.

Batch leaching tests conducted on the ash-amended pavements indicatedthat certain COPC (Al, Mo, Sb) were found to leach above the regulatoryrisk thresholds used in this assessment. For the PCC pavements, thecontrol samples were also found to leach concentrations of theseelements above GCTLs, indicating that no additional COCPs were createdby the inclusion of the BA. Ash-amended HMA did leach Sb, inconcentrations less than an order of magnitude over its GCTL which wasnot seen in the control samples. The crushed material form used in theSPLP test would be a conservative method of estimating COPC release whenthe material is placed as a pavement, but may provide important data onelement release if the pavement materials were to be crushed or milledfor reuse or disposal. In these types of applications, appropriateconsiderations for the management of these residues would need to betaken into evaluation. Weathering of pavements over their lifetime wouldlikely result cracking and an associated increase in exposed surfacearea. However, as the material would still be in a monolithic, insteadof a granular form (e.g. a milled pavement) the calculated flux from the1315 test (mass leached/area) could still be used as a inputconcentration provided the increase in exposed surface area (due tocracking) was accounted for appropriately.

3.2 Element Release from Monolithic Pavements

EPA Method 1315 was conducted to evaluate COPC release from thepavements in their intact form to: (i) quantify the differences inrelease between ash-amended PCC and HMA (ii) provide a comparison of thecumulative mass release [M_(Cumu)(mg-COPC/kg-dry-pavement)] between themonolith and the batch tests, (iii) assess the mechanisms of elementrelease from the pavements (diffusion, dissolution), and (iv) determinethe D^(obs) and LI to quantify the release rates of diffusion controlledelements.

The pH of the control PCC concrete pavements (in the monolith test)began at a mean value of 10.25 (day 0.08) and decreased throughout thecourse of the test to a final pH of 8.65 (day 63); this was similar tothe trend observed in the ash-amended PCCs, where the pH began at 10.20(day 0.08) and decreased to a final pH of 8.85 (day 63). FIG. 8 presentsthe method 1315 pH and COPC leaching data for the PCC pavements. Similarto the results of the SPLP test Sb was not detected in any of the PCCsamples despite the decrease in pH seen throughout the test. Sb may bewell encapsulated in the PCC matrix. Pb was not measured in the method1315 test, and the release of Pb from the batch tests could be relatedto the increased surface area of the PCC (due to size reduction) or theincreased pH of the batch extractions.

FIG. 9 displays the pH and COPC concentrations for the HMA asphaltpavements. The pH values for the control and ash-amended HMAs becamemore acidic over time. The pH of the HMA pavements in the monolith testdisplayed a different trend seen for the HMA pavements in the SPLP; forthe monolith test, the pH values for the ash-amended and control sampleswere similar.

For both the control and ash-amended HMA, the concentrations of Al werefound to be above the GCTL in all instances. Leached Al concentrationswere higher for the ash-amended HMA with respect to the control;however, the large discrepancy in leached concentrations (over an orderof magnitude) between the control and ash amended samples (seen in theSPLP) was not observed in the monolith test. The pH differences betweenthe monolith and SPLP test could be one of the factors that resulted inlower concentrations of Al leached in the monolith test. Similarities inpH between the ash-amended and control monoliths highlight that otherfactors besides pH (i.e. the concentrations of Al contained in thesamples and potentially the speciation of the Al in the pavement) maycontribute to the increased Al leaching seen in the ash-amended HMA.Concentrations of Sb in the ash-amended samples were found to be abovethe GCTLs for half of the leaching intervals (FIG. 9 ). As a generaltrend, leached concentrations of Sb increased over time. For all of theleaching intervals, Sb concentrations were within the same order ofmagnitude as the GCTL. Mo and Pb leaching from the ash amended HMA wassimilar to the results seen in the SPLP extractions, Pb was found toleach below detection limits in all intervals and Mo was measured in lowconcentrations throughout the course of the tests.

3.2.1 Cumulative Mass Release in Batch and Monolith Testing

FIG. 3 presents the M_(Cumu) of Al for the ash-amended and controlpavements (HMA and PCC) in Method 1315. For comparison, the cumulativemass release (mg/kg) from the SPLP tests is provided in FIG. 6 .

The cumulative release of Mo from the PCCs in Method 1315 was found tobe similar (0.262 mg/kg—ash-amended, 0.255 mg/kg—control) for both ofthe pavements (ash and control); this data, along with the data seen inthe SPLP test, suggest that the leaching of Mo may primarily be fromcomponents of the PCC and not a result of the addition of the BA intothe PCC matrix. Previous study on the leaching of recycled PCC aggregate(RCA) by Engelsen et al., (2010) found Mo release (in the same pH regionobserved here) to be within the same order of magnitude as the valuesmeasured in the monolith leaching test [42].

Sb M_(Cumu) from the monolithic sample (0.172 mg/kg) was again differentthan the SPLP test (0.701 mg/kg), despite a lower pH that might be moreconducive to the leaching of Sb as an oxyanion. In all instances,leaching the pavements in their monolithic form can result in asubstantial reduction in element release in comparison to the batchtests. A large pH difference was not seen for the monolith; this may beone factor that resulted in less of a difference in M_(Cumu) between theash-amended and control HMAs. The similarity in the measured pH valuesfor both the HMA samples could be related to the fact that the BA isencapsulated during the monolith test, while once the sample issize-reduced (for the SPLP), a portion of the BA could become exposedresulting in the observed increase in pH.

3.2.2 Release Mechanisms for COPC in HMA and PCC Pavements

The results of Method 1315 demonstrate that the release of COPC from thepavements could be markedly reduced if the materials were contacted withwater in their monolithic form. To determine the release mechanisms forthe COPC present, an approach developed by De Groot and Van der Slootwas employed [48]. Similar approaches have been used to evaluate therelease mechanisms for a number of stabilized waste produces [28, 36,38].

First, a graph of the M_(i) and the cumulative leaching time was plottedon a log-log scale; next the slope of the line was determined throughregression analysis. The slope was then used as an indicator of theleaching mechanism present; for diffusion to be indicated as thegoverning release mechanism, the slope of the line needs to fall between0.35 and 0.65. A slope of greater than 0.65 indicates dissolution, whilea slope less than 0.35 indicates depletion as the dominant form ofrelease [25, 38, 48]. The first leaching interval (0.08 days) wasomitted from the regression analysis as it was not conducted for all ofthe pavement types.

FIG. 4 presents the log-log comparison of M_(i) and the cumulativeleaching time for Al release from the PCC pavements. The slope of linesand the R² values are indicated in the figure. In all instances, the R²values were greater than 0.94, indicating a good fit of the regressionto the measured data points. For all of the pavements tested (HMA andPPC), the release mechanism for Al may be indicated as diffusion; Sbrelease from ash-amended HMA may also be found to be governed bydiffusion (R²=0.991, Slope-0.519). Shown in FIG. 5 is the log-logcomparison and regression analysis for Mo release from the PCCpavements. For both the ash-amended and control pavements, depletioncould be the dominate release mechanism, as the slopes of both lineswere less than 0.35. These result supports that Mo release may berelated to components in the PCC. The release of Mo can be found to begoverned by depletion from the material, and not by the diffusion of theelement through the PCC matrix. Galvin et al. (2014) evaluated leachingof concrete produced with recycled aggregates and found the slope in thelater stages of a tank leaching test to be similarly governed bydepletion [49]. If Mo release were to be attributed to the inclusion ofthe BA, it may be expected to be released through diffusion, as the BAis encapsulated within the PCC matrix.

Diffusion can be the primary release mechanism for waste materialsencapsulated in PCC or treated with S/S [28, 30]. This can support thetrends seen for Al in all pavement types as the inclusion of the BA wasnot found to change the dominant release mechanism in any instance.There are limited data available related to the release mechanisms forwaste materials encapsulated in HMA pavements. It is important to notethat the slope of the regression line for the control and ash amendedHMA did increase from 0.42 (control) to 0.606 (ash-amended HMA). This isconsistent with the increased LI seen for the ash-amended HMA and couldsuggest that other WTE BA samples could potentially result in a changeto the Al release mechanism present. Release due to diffusion, seen forSb (in the ash-amended HMAs) illustrates that Sb mass transfer can occurby the migration of Sb through the pore structure of the HMA (driven bya concentration gradient), the dominant mechanism of constituent releasethat can be present in other methods of waste encapsulation.

3.2.3 Observed Diffusivity (D_(i) ^(obs)) and Leachability Index (LI)

FIG. 10 presents the min, max, and mean values of the LI and D_(i)^(obs) for Al and Sb for the ash-amended HMA. The diffusion coefficientsfor Sb in the ash-amended HMA pavements ranged from 1.66×10⁻¹⁰ to2.87×10⁻⁹ cm²/s, when classified using the LI these values fell between8.5 and 9.75. Based on the results of the LI the mobility of Sb in theHMA can be characterized as low (LI>8).

Although both of the LI's (ash-amended and control HMAs) indicated thatAl release from diffusion may be limited, there was an observableincrease related to the addition of the BA. These results support thatthe inclusion of the BA (into the HMA) can facilitate an increase in Alrelease and mobility. For the PCC pavements the LI and D^(obs) valuesdid not vary dramatically between the ash-amended and control sampleswith mean values on the order of (1×10⁻¹² cm²/s). Therefore, thediffusivity of Al in the PCC matrix may not be substantially affected bythe BA addition.

The calculated Lis for the COPCs were found to be below the thresholdfor low mobility. With respect to Sb, this supports the results of theMethod 1315 test, which indicate that the release of Sb into theenvironment could be limited when material is in its monolithic form. Almobility was also low, however, differences in LI and D_(i) ^(obs) wereobserved between the ash amended and control HMAs, supporting thedifference in cumulative Al release can be seen in the monolith leachingtest.

4.0 Conclusions

Overall, encapsulation of the BA in the PCC matrix proved encapsulationcan be a suitable method of reducing the leachability of COPC from theash. HMA samples amended with WTE BA can exhibit a certain degree ofleaching, however, results from this study support that when in itsmonolith form, element mobility from the pavements could be verylimited. It is important to note that all leaching tests are designed astools to determine the magnitude of aqueous release for a particularmedia (e.g. WTE amended pavement). These concentrations can then be usedin a fate and transport evaluation to assess environmental risk, whichcould be heavily dependent on the site hydrogeologic conditions (e.g.aquifer depth and thickness) and construction practices. Therefore, itis recommended that this type of evaluation be conducted, prior tobeneficial use of these materials in practice. This study illustratesthat both PCC and HMA used as a partial aggregate replacement inpavement construction can encapsulate potential COPC within the pavementmatrices to some degree.

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The BA sample used to produce the ash-amended pavements can be screenedwithin the facility to remove any materials smaller than 9.5 mm, thenfurther screened to remove particles greater than 19.05 mm. This can beperformed so that the ash can achieve the appropriate gradation for usein HMA, and to help mitigate issues related to hydrogen gas formation inPCC. An example of grain size distribution according to the presentcompositions and methods can be seen in FIG. 11 . Examples of roadwayconstruction using the present compositions and methods can be seen inFIGS. 12 and 13 . Embodiments of PCC and HMA mixtures using compositionsand methods as described herein can be seen in FIGS. 14, 15 (a), and15(b).

SI Section 1.2 Equations Used to Calculate Release from Method 1315

The cumulative mass release (M_(Cumu.)-mg-element/kg-pavement) ofelements from the monoliths were calculated using Equation 1 belowwhere: M_(Cumu.) is equal to the sum of the measured leachateconcentrations at each time interval (C_(i)-mg/L) multiplied by thevolume of the tank (V_(tank)) and divided by the dry mass (m_(dry)) ofthe pavement sample. The elemental mass flux of the monoliths wascalculated using Equations 2 and 3 below. First the mass release perexposed surface area (M_(i)) of each collection period was determinedusing Equation 2 below where: V_(tank) is the volume of the extractionsolution in the tank (C and SA have been previously defined). M_(i) wasthen divided by the interval leaching time (seconds) to calculate theflux, as shown in Equation 3 below. To calculate the observed elementaldiffusivity from the pavement samples, an analytical solution derivedfrom Crank (1975) [37] for diffusion from a cylinder into a infinitebath (of zero concentration) was used (Equation 4, as shown below). Inaddition to variables that have been previously defined (M_(i), t), thedry density of the sample (p), and the initial concentrations of thetrace elements (C₀— determined using EPA Method 3050b and the approachin Section 2.2) were used in the calculation. C₀ concentrations can befound in FIG. 7 , and are discussed previously. The dry density andexposed surface area values for the pavements are provided in the SIsection. For each pavement, the D_(i) ^(obs) was calculated for eachleaching interval; a minimum, maximum, and mean value were then obtainedand these were used to calculate three values for the LI. Pavement drydensity and exposed surface area data according to embodiments of thepresent disclosure and EPA method 1315 can be seen in FIG. 16 . Datarelating to leached elements in SPLP and total concentrations of leachedelements in SPLP test in embodiments of the present disclosure can beseen in FIG. 17 . FIG. 18 shows the total environmentally availableconcentrations of trace elements in embodiments of ash-amended andcontrol pavements according to the present disclosure.

Equations

$\begin{matrix}{M_{c{{umu}.}}\  = {\Sigma\left\lbrack {C_{sample}*\frac{V_{tank}}{m_{dry}}} \right\rbrack}} & {{Eq}.1}\end{matrix}$ $\begin{matrix}{M_{i} = \left\lbrack \frac{C_{i}*V_{tank}}{SA} \right\rbrack^{\text{.5}}} & {{Eq}.2}\end{matrix}$ $\begin{matrix}{F_{i} = \frac{M_{i}}{T_{i} - T_{i - 1}}} & {{Eq}.3}\end{matrix}$ $\begin{matrix}{D_{i}^{obs} = {\pi\left\lbrack \frac{M_{i}}{2\rho{C_{0}\left( {\sqrt{t_{i}} - \sqrt{t_{i - 1}}} \right)}} \right\rbrack}^{2}} & {{Eq}.4}\end{matrix}$

Example 2

1.0 Introduction

The beneficial use of waste-to-energy (WTE) bottom ash (BA) as aconstruction material has been a significant focus of civil andenvironmental researchers for the past several decades [1-7]. Becausethe particle size of the ash is similar to that of most conventionalpavement aggregates, reuse in road construction projects is often citedas the most practical beneficial use application. In many countries,including the United States, WTE BA represents a relatively high volumematerial stream that is normally landfilled and could be acquired at areasonably low cost. This provides an additional incentive for recycling[8]. The beneficial use of WTE BA in construction applications aroundthe world have focused on use as a road base [9, 10] as well as the useof BA as an aggregate in Portland cement concrete (PCC). However use inPCC has been challenging in some instances as components within the ashcan cause deleterious effects within the concrete matrix to some degree[6, 7, 11, 12].

Aging of WTE BA has been cited as a method of reducing the leaching ofcertain trace elements, particularly Pb, from the material prior tobeneficial use. Because BA is heated and then rapidly cooled in aquench, it is classified as a meta-stable material and as the ash agesit reacts with atmospheric carbon dioxide to produce new mineral forms.WTE bottom ash is known to contain large percentages of Ca by mass(5.0-10%), carbonation of WTE bottom ash can occur through the reactionof atmospheric CO₂ with Ca in the bottom ash, resulting in theproduction of calcite (CaCO₃) [5, 8, 13]. Although aging the ash can beessential in creating in an environmentally stable product for reuse asa road base course, encapsulation within a PCC matrix can reduce theleaching of trace elements from WTE ash as well as other combustionresiduals [14-16]. The logistical and operational costs associated withthe aging of WTE BA could be significant when conducting a full-scaleconstruction project; the concept of fully encapsulating WTE BA inconcretes provide benefit, as many of the environmental concernsassociated with use in an unencapsulated application (such as a roadbase) would be mitigated. Thus, the question has been posed as to theimpacts (if any) the generation of these secondary mineral forms in theaging process might have on the material properties of the ash-amendedproduct. One of the key concerns is that as the BA hydrates and producesthese secondary mineral forms, the expansion of the ash within PCC couldcreate stresses that result in cracking. Because relative amounts ofmany of the mineral forms present in fresh and aged WTE BA could differ,the impact of this on ash-amended concrete strength and durability canbe assessed.

Some of the factors that have been cited as adverse effects related tothe use of WTE BA in PCC include: decreased compressive strength,increased risk of alkali-silica reaction (ASR), and the formation ofhydrogen gas. Reaction of metallic aluminum with the hydroxidescontained in the Portland cement has been demonstrated to producehydrogen gas; in a basic environment Al reacts to form aluminate (AlO₂⁻) while liberating H₂ [6, 7, 11, 12, 17]. The voids formed by the gashave been shown to contribute to a decrease in the compressive strengthof the material [7, 12]. Additionally, Muller and Rubner hypothesizedthat the one of the primary reasons for the degradation of the concreteamended with WTE BA was due to the reaction of deleterious (glass andaluminum) compounds in the ash. However, the concrete mixture used inthe research, incorporated a relatively high water to cement ratio (W/C)(0.65) and did not utilize mineral admixtures, such as coal fly ash[12]. Accordingly, the mix used by Muller and Rubner was moresusceptible to degradation due to the relatively high permeability(because of the elevated W/C) and the absence of mineral admixtures thatare known to reduce permeability of concrete [18, 19].

The example herein investigates methods (e.g. use of mineral admixtures,size fractionation of ash) that could help reduce some of the problemsassociated with the use of WTE BA as a partial aggregate replacement inPCC. The impacts of aging of the ash itself, were evaluated through theuse of a lab-scale accelerated carbonation process. Acceleratedcarbonation experiments simulate long-term ash exposure to atmosphericCO₂ over shortened time scales, and have been used by concreteresearchers, as well as scientists examining the properties of wastecombustion residues [20-22]. The occurrence of carbonation can beverified by measurement of the pH of the ash when immersed in water, asthe alkaline calcium minerals are known to be depleted throughcarbonation resulting in a decrease in mineral pH [5, 23]. Compressivestrength testing from ash-amended and control concretes was performedand surface resistivity and length change testing were conducted toevaluate the impact of WTE BA addition on the relative durability andreactivity of ash-amended concretes. These data are useful forengineers, scientists, and practitioners.

2.0 Materials and Methods

2.1 Ash Description and Sample Collection

WTE ash samples were collected from a 1,000 ton per day mass burn WTEfacility in Florida, US. Two different size fractions of the BA werecollected. The facility sampled utilized municipal solid waste from thesurrounding communities as a feedstock, employs a moving grate typeboiler for combustion, and operates at an approximate combustiontemperature of 1,000° C. Both BA fractions were sampled followingferrous and non-ferrous metals recovery. The facility sampled,size-separates their BA in-process, using a 9.5 mm screen, followingseparation the material greater than 9.5 mm is passed through aconventional eddy current separator to recover non-ferrous metal. Noadvanced non-ferrous metal recovery technologies were employed on thefraction of the material finer than 9.5 mm. The two samples collectedrepresent the fraction retained on the 9.5 mm screen and the fractionpassing through it. A composite sample of each ash size fractions [lessthan 9.5 mm (LT-9.5) and greater than 9.5 mm (GT-9.5)], was generatedfor a period of 7 days. To produce the composite sample, sub-samples (ofeach size fraction) were collected every 30 min for 2 8-hour intervalseach day. These 14 samples were then combined in a large baffled mixerand rotated for a period of 30 minutes to produce the composite sample(for each size fraction). The GT-9.5 ash was then further screened toremove any particles larger than 19.05 mm (since these particles may notbe suitable for use in concrete applications). BA samples were thenstored in sealed 19 L buckets until time of use. Following screening atotally environmentally available acid digestion was conducted on theash flows to ascertain the concentration of aluminum in the bottom ash(mg/kg-dry). This acid digestion was conducted in accordance with EPAmethod 3050b, fourteen replicates of each sample were tested [24].

The coal fly ash employed as an admixture in the PCC was purchased froma local vendor, and previously sourced from a coal-fired powergeneration facility. The coal fly ash used conformed to all of thespecifications for Class F coal fly ash outlined in ASTM C618 StandardSpecification for Coal Fly Ash and Raw or Calcined Natural Pozzolan forUse in Concrete [25]. These specifications include: a total mineralcomposition of SiO₂, Al₂O₃, and Fe₂O₃ greater than 70% by mass, maximumSO₃ content of 4.0% (by mass), maximum moisture content of 3%, andmaximum loss on ignition of 6%. In accordance with ASTM C618 thephysical requirements for Class F coal fly ash include: <34% of thematerial retained on a 45 um (No. 325) sieve when wet-sieved (with avariation of less than 5% points from average), a strength activityindex (done in accordance with ASTM C311) of 75% or greater whencompared to the control cements at 7 and 28 days, and a waterrequirement of less than 105% of the control.

2.2 Aggregate Characterization, Concrete Batching, and Mix Design

The aggregates for the concrete and the WTE BA were evaluated forspecific gravity, adsorption, and percent loss by Los Angeles abrasion(LA loss) in accordance with ASTMs C127 and C131 respectively [26, 27].For the LA abrasion testing the number of charges and the particle sizefractions tested are based on the initial particle size distribution ofthe aggregate being evaluated. For the GT-9.5 material a B grade (2.5 kg19.05 mm-12.5 mm; 2.5 kg 12.5 mm-9.5 mm) was selected, as the LT-9.5material had a finer particle size distribution, a C grade (2.5 kg 9.5mm-6.35 mm; 2.5 kg 6.35-4.75 mm) was utilized.

Concrete specimens were prepared in the laboratory in accordance withASTM C192. The course aggregate and 50% of the total volume of the mixwater were first added to the mixer while stationary, the mixer was thenstarted and the fine aggregate and cement added, finally the remaining50% of the mix water was then added. The sample was then mixed for aperiod of 3 minutes, allowed to rest for 3 minutes, and then mixed foran additional two minutes. The sample was then discharged to a pan andremixed with a trowel to eliminate segregation. Both the (10.16cm-dia×20.32 cm-height) cylinder molds and the (152×152×559 mm) beammolds used for length change testing were compacted using a vibratoryeffort until large air bubbles were not visible. Samples were removedfrom all molds 24±8 hours after casting [28].

Control and ash-amended concrete specimens were produced using the samemix design (provided in FIG. 19 ), except that a portion of the coarseaggregate was replaced with WTE BA, and the volume of mix water wasadjusted to account for differences in aggregate adsorption whilepreserving a constant w/c for each mix. A grain size distribution ofboth ashes is contained in FIGS. 29 and 30 . The virgin aggregate usedin the study was Florida lime rock, a typical aggregate used in concreteproduction in the southeastern U.S. The lime rock conformed to thegradation requirements of an American Association of State and HighwayTransportation Officials (AASHTO) #57 stone, a table containing thegradation requirements for an AASHTO #57 stone is provided in the SIsection below [29].

2.3 Concrete Compressive Strength Testing

All concrete tests were conducted in triplicate; 12 cylinder molds andthree beam molds were produced for each of the concrete mixes.Subsequent to mixing, and the initial 24 hour curing period, the sampleswere immersed in a lime water Ca(OH)₂ curing solution per therequirements of ASTM C192 until the time of testing [28]. Compressivestrength testing was conducted in accordance with ASTM C39 [30].Compressive strength testing was performed on a hydraulic compressionmachine and run on laboratory batch specimens at ages of 3, 7, 28, and56 days.

2.4 Accelerated Carbonation

Accelerated carbonation experiments were conducted on the GT-9.5 ash,because of the initial strength results of the mixtures produced usingthe LT-9.5 ash this sample was omitted from further testing. The pH ofthe ash when immersed in reagent-grade water (water with a measuredresistivity of >18.2 MΩ·cm) was used as a surrogate indicator ofcarbonation. Numerous published studies have demonstrated that calciumspecies present in the WTE BA (portlandite, gibbsite, ettrinigite,calcite) control the pH, and that this pH is reduced through carbonation[5, 31]. The pH can be reduced as the species buffering the pH of the BAat highly alkaline values (portlandite, ettringite) are depleted duringcarbonation (transformed primarily to calcite). These reactions not onlyaffect the geochemical structure but can decrease trace elementleachability [5, 31]. Approximately 25 kg of the GT-9.5 ash was placedin a sealed chamber lined with low-density polyethylene. Perforatedtubing was placed within the ash, to allow the CO₂ to diffuse throughthe material, and the chamber was filled with a 100% CO₂ atmosphere fora period of 4 days. The pH of the BA when immersed in reagent water wasmeasured prior to (pH=10.5) and following carbonation (pH=9.1). Thisreduction in pH was used to demonstrate that carbonation of the BA hadoccurred. The exact amount of time that would be required for these pHchanges to occur in a natural setting was not determined. However, otherpublished literature indicates that the pH changes seen for the sizefractions carbonated would be expected to occur over a number of monthsdepending on the local conditions [23, 32]. Chimenos et. al found thatthe 6-16 mm size fraction of WTE BA from a Spanish WTE facilitydecreased from a pH of approximately 10.8 to a pH of 10.0 over theperiod of 170 days [32]. Arickx et al., (2006) found that the finefraction of WTE BA (0.1-2 mm) decreased in pH from 12.1 to 10.7 after aperiod of three months of natural aging, and stated that three monthswas a sufficient time interval to decrease the pH of the 2-6 mm and 6-50mm fractions to a value where elements would leach below Belgianstandards (although the final pH values of the larger fractions were notreported) [23].

2.5 Concrete Length Change and Surface Resistivity

Concrete length change testing was conducted on the ash-amended andcontrol PCC mixes to assess changes caused by factors other than appliedexternal force or temperature. All concrete length change testing wascompleted in accordance with ASTM C157 [33]. Length change testingoccurred under both dry and wet conditions. Specimens subject to drystorage were stored in an environmental chamber with a set relativehumidity of 50±4% and a temperature of 73±3° F. (22.7±1.66° C.) (perASTM 157). All length change tests were conducted for a period longerthan 365 days. Surface resistivity testing was employed to assess therelative permeability of the ash-amended concretes and to examine theconcrete's resistance to chloride ion penetration, in accordance withAASHTO TP-95. Specimens were tested in triplicate using a concreteresistivity meter at 6 intervals over a period of 92 days.

3.0 Results and Discussion

3.1 Preliminary Strength Testing

An uncarbonated sample of the LT-9.5 BA was used to replace 10, 20, and30% of the course aggregate in a series of PCC mixes. The 28 daycompressive strength results for the LT-9.5 and GT-9.5 ash mixes areshown in FIGS. 21 and 22 . The measured LA loss for the LT-9.5 (38%) andGT-9.5 (42%) ash (FIG. 20 ) did meet the specification of 45% set by theFlorida Department of Transportation, indicating it can have suitablestrength for use as an aggregate in PCC [34].

The GT-9.5 ash was used to produce a series of PCC mixes where 25%, 50%,and 75% of the coarse aggregate was replaced with BA. In thisexperiment, an uncarbonated ash sample was used. The compressivestrength of the ash-amended mixes were lower than that of the controlmix. The 28 day strength for the GT-9.5 ash-amended and controlspecimens is shown in FIG. 2 . As the aggregate replacement percentageof ash added increased, the resulting compressive strength of the PCCcan change. The compressive strength changes measured for the GT-9.5 ashwere not as substantial as the strength changes seen for the PCC amendedwith the LT-9.5 ash.

A number of authors have suggested hydrogen gas can be produced duringthe early phases of hydration for concretes amended with WTE BA; theseauthors cite that reaction can occur between aluminum in WTE BA ash andhydroxides found in the concrete as a mechanism of gas production [7,12, 35, 36]. This reaction can decrease strength (due in part to anincrease void space within the hardened cement paste) as well asspalling for conditions where aluminum is present near the surface ofthe concrete [7, 12, 35]. Hydrogen gas formation is a mechanism that canreduce the strength in the LT-9.5 ash mixes.

At a typical WTE facility (including the facility where the BA wassampled), non-ferrous metals (primarily aluminum) can be recovered fromthe ash following combustion by utilizing an eddy-current separator [37,38]. The eddy-current separator can remove a percentage of the aluminumfrom the ash, but a significant fraction can remain in the waste streamfollowing processing. Grosso et al., reported average eddy currentseparator efficiencies of approximately 30% and indicated that majorityof the remaining aluminum can be concentrated in the smaller sizefractions (<12 mm) as eddy current separators can increase in efficiencywith increasing particle size [37]. A 2013 study conducted by Biganzoliet al. (2013) reported Al concentrations in the range of 8% by mass forthe fine (<4 mm) fraction of BA [38].

The results of the total environmentally available digestions found thealuminum content for the GT and LT material can be 2.6% and 3.3%respectively. Note that the results of the EPA 3050b test do notdifferentiate between metallic Al and mineral Al, such as the aluminumcontained in ettringite (Ca₆Al₂(SO₄)₃(OH)₁₂·26H₂O), a calcium basedaluminosulfate known to be contained in WTE ash. However, they canprovide a reference concentration for total aluminum (for comparison toother studies) as well as a quantitative indicator that the LT fractioncan contain more total aluminum. As the LT-9.5 ash can contain a higherpercentage of fine material than the GT-9.5 ash, it may also contain ahigher percentage of metallic Al. This could result in the impact ofhydrogen gas production (in the LT-9.5 ash-amended mixes) being greater,and may decrease the compressive strengths. The strength of the LT-9.5ash mixes could be improved by better processing the ash to improve thenon-ferrous metals recovery rate.

The results from the compressive strength testing indicate that sizefractionation of the WTE BA can be important with regard to theconsideration for use in as an aggregate in PCC. The larger fraction,which serves as replacement for coarse aggregate (19.05 mm-9.5 mm) canachieve suitable compressive strength. However, the LT-9.5 fraction, wasunable to achieve suitable compressive strength even at low replacementpercentages, and it was excluded from further testing accordingly.

3.2 Impacts of Aging

To examine the impacts of ash aging, a series of PCC mixes were producedusing ash that had been carbonated in accordance with the procedureoutlined in Section 2.4. The GT-9.5 ash was utilized as partial courseaggregate replacement (25%, 50%, and 75% of the course aggregate) in thelaboratory mixes. For the purposes of comparison, uncarbonated ash mixeswere batched at the same replacement percentages as well as a controlmix, which contained no ash. Compressive strength, surface resistivity,and length change testing were conducted on the carbonated anduncarbonated ash samples.

3.2.1 Compressive Strength

The results of the compressive strength testing of the control andexperimental specimen groups amended with the carbonated anduncarbonated ash concretes are presented in FIGS. 23 and 24 . At 28days, the carbonated ash concretes yielded mean compressive strengths of19.4, 21.8, and 26.9 MPa for the 75%, 50%, and 25% replacementsrespectively, and the uncarbonated samples produced mean compressivestrengths of 17.2, 20.7, and 29.2 MPa for the 75%, 50%, and 25% ashconcretes.

3.2.2 Concrete Length Change

To evaluate the reactivity of the WTE BA, concrete length change testingwas conducted. Previous researches have cited hydrogen gas formation [7,12, 36] as well as ASR [12] (due to the glassy fraction of the BA) aspotential expansive effects related to using WTE BA in PCC. This issupported by the results of the 56 day compressive strength testing inthe ash amended samples. Coal fly ash is known to decrease expansion dueto ASR [39-41] and can be included in the concrete mix design to offsetpotential deleterious effects of ASR in the concrete. Both wet and drylength change testing was conducted for specimens produced using boththe carbonated and uncarbonated WTE BA. A total of seven experimentalmixes were tested, the carbonated and uncarbonated GT-9.5 ash were eachused as a 25%, 50%, and 75% percent replacement of the coarse aggregate,and a control mix without ash was also produced for reference.

Specifications related to concrete length change vary between state andcountry. As a relative indicator of the magnitude of the changesobserved, the Florida Department of Transportation (FDOT) has currentlyset a concrete length change standard for concrete used in repair (usingASTM C157) of 0.12% at 28 days; the maximum measured change (50%uncarbonated sample—0.032%) was less than 30% of this value. Thresholdsfor ASR are often set based on expansion tests that rely on theimmersion of the samples in a NaOH solution (ASTM 1260, CAN/CSAA23.2-14A). [42, 43] These tests were not conducted, so a directcomparison is not applicable; however the measured wet length change at110 days was substantially lower than the guidance set by ASTM C1260 of<0.1% within 14 days.

The results of the dry length change testing for the carbonated anduncarbonated ashes are presented in FIGS. 25 and 26 respectively. Drylength change testing did not produce the high percentages (>0.12%) ofexpansion that would be attributed to H₂ formation or ASR. It ispossible that the addition of the CFA may have contributed to the lackof expansion as CFA has been cited as a mechanism of reducing ASR due toa denser pore structure and a reduction in available alkalis consumedduring the pozzolanic reaction [44, 45]. Additionally, the larger sizeof the ashes may have limited the total surface area available forreactivity, further research incorporating analysis of the concretemicrostructure would be needed to confirm these hypotheses; othermechanisms to reduce ASR such as metakaolin addition can also beevaluated as to their effectiveness. Possible mechanisms for controllingexpansion in WTE ash-amended concretes include limiting ash replacementpercentages and utilizing a mineral admixture (CFA) that is known toreduce ASR [19].

3.2.3 Surface Resistivity

Surface resistivity testing was conducted on PCC specimens producedusing the GT-9.5 ash. Similar to length change and compressive strengthtesting, seven PCC samples were tested (carbonated and uncarbonated BAas a 25%, 50%, and 75% course aggregate replacement, and a control).Surface resistivity testing was used to evaluate differences in thedurability (relative permeability and resistance to chloride ionpenetration) between the carbonated and uncarbonated ash concretes andto assess variances between the ash-amended concretes and the control.It is know that the addition of pozzolans to PCC can result in increasedsurface resistivity and resistance to chloride ion penetration [45, 46].Therefore this test provides an additional indicator of the evidence ofa pozzolanic activity related to the addition of the WTE BA.

The surface resistivity (kΩ-cm) of the uncarbonated and carbonated ashconcretes are plotted as a function of time in FIGS. 27 and 28 ; data onthe control surface resistivity is provided for reference in eachfigure. As expected, the surface resistivity of all of the samples canincrease with time, due to the densification of the concretemicrostructure. Tanesi and Ardani, and Kessler et al. compared valuesfrom the chloride ion penetration test (ASTM C1202) [also known as therapid chloride permeability test (RCPT)] to measured surfaceresistivities from a myriad of difference concrete mixtures to develop arelationship between surface resistivity and RCPT [47, 48]; based onthese relationships, the majority of the measured values (for all of thesamples) were found to have a moderate resistance to chloride ionpenetration (12-21 kΩ-cm or 2,000-4,000 coulomb for ASTM C1202).

In all instances, surface resistivity values for the carbonated ashconcretes were found to be similar to or elevated above the controlsample. There were no substantial differences in measured surfaceresistivities between the carbonated and uncarbonated ash-amendedsamples, although the carbonated samples did display a trend ofincreasing resistivity with increasing ash replacement percentage. In 5out of the 6 ash-amended samples tested, the surface resistivities werefound to be higher than the measured values for the control. Based onthe resistivity trends seen for other SCM [45, 46] these results provideevidence of a pozzolanic reaction, related to the addition of the WTEBA. This is further substantiated by the trend of increasing surfaceresistivity with increasing ash replacement percentages seen for thecarbonated ashes.

Surface resistivity testing of the ash-amended concretes demonstrated nosubstantial difference in resistivity with respect to carbonation of theBA. These results indicate that the aging of WTE BA may not affect thematerial properties of PCC when BA is included as a coarse aggregatereplacement. When comparing the surface resistivity data of theash-amended concretes to the controls, the majority of the samplesyielded a slightly higher surface resistivity. This suggests thepotential for pozzolanic activity related to the addition of the ash. Asleaching risk is an important consideration for concretes containing WTEBA, and leaching is function of the amount of water in contact with thematerial, these tests provide some evidence that the permeability of WTEBA amended and control concretes may not be expected to be significantlydifferent.

4.0 Conclusions

The incorporation of WTE bottom ash into PCC as a partial aggregatereplacement can have an impact on concrete compressive strength. Impactsfor both of the BA size fractions tested (LT-9.5 ash, GT-9.5 ash) can beseen. In the case of the LT-9.5 ash, differences in strength can be seeneven at low replacement percentages; this may attributed to theformation of H₂ gas within the concrete microstructure (cited by anumber of other authors in previous studies [6, 7, 12]). This effect maybe amplified due to the higher percentage of Al (and its relativelylarge surface area) contained in the smaller size fraction of the ash.Concrete specimens batched with only the GT-9.5 size fraction of the ashwere found to perform suitably at low replacement percentages (<25%) andcan exceed the 28-day design strength set for the control mix design.Carbonation may or may not significantly affect the physical propertiesof the WTE BA amended concretes. All ash-amended samples were found tohave different properties than that of the controls, but can becomparable to controls at low replacement percentages. Length changetests illustrate the potential benefits of using a mineral admixture toreduce the potential for expansion caused by the inclusion of the ashaggregate. The results of this study suggest that WTE BA could be aviable option for use as a partial course aggregate replacement with orwithout being aged, provided that appropriate measures are taken tomitigate reactivity and meet strength requirements.

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Ratios, concentrations, amounts, and other numerical data may beexpressed in a range format. It is to be understood that such a rangeformat is used for convenience and brevity, and should be interpreted ina flexible manner to include not only the numerical values explicitlyrecited as the limits of the range, but also to include all theindividual numerical values or sub-ranges encompassed within that rangeas if each numerical value and sub-range is explicitly recited. Toillustrate, a concentration range of “about 0.1% to about 5%” should beinterpreted to include not only the explicitly recited concentration ofabout 0.1% to about 5%, but also include individual concentrations(e.g., 1%, 2%, 3%, and 4%) and the sub-ranges (e.g., 0.5%, 1.1%, 2.2%,3.3%, and 4.4%) within the indicated range. In an embodiment, the term“about” can include traditional rounding according to significant figureof the numerical value. In addition, the phrase “about ‘x’ to ‘y’”includes “about ‘x’ to about ‘y’”.

Unless defined otherwise, all technical and scientific terms used havethe same meaning as commonly understood by one of ordinary skill in theart to which this disclosure belongs. Although any methods and materialssimilar or equivalent to those described can also be used in thepractice or testing of the present disclosure, the preferred methods andmaterials are now described.

Embodiments of the present disclosure will employ, unless otherwiseindicated, techniques of separating, testing, and constructingmaterials, which are within the skill of the art. Such techniques areexplained fully in the literature.

It should be emphasized that the above-described embodiments are merelyexamples of possible implementations. Many variations and modificationsmay be made to the above-described embodiments without departing fromthe principles of the present disclosure. All such modifications andvariations are intended to be included herein within the scope of thisdisclosure and protected by the following claims.

The invention claimed is:
 1. A composition comprising: Portland cementconcrete; and a waste-to-energy bottom ash (WTE BA) aggregate fraction,wherein the WTE BA aggregate fraction consists of WTE BA aggregates ofabout 9.5 mm to about 19.05 mm in size, wherein the aggregate fractionhas an aluminum content of about 25,000 mg/kg dry or less.
 2. Thecomposition of claim 1, wherein the Portland cement concrete comprisesType I Portland cement, Type II Portland cement, or a combinationthereof.
 3. The composition of claim 1, wherein the Portland cementconcrete comprises tricalcium silicate, dicalcium silicate, tricalciumaluminate, tetracalcium aluminoferrite, free calcium oxide, sulfurtrioxide, or any combination thereof.
 4. The composition of claim 1,wherein the aluminum content is determined using EPA testing method3050b.
 5. The composition of claim 1, wherein the WTE BA aggregatefraction is about 50% or less of the total composition.
 6. Thecomposition of claim 1, wherein the WTE BA aggregate fraction is fromabout 25% to about 50% of the total composition.
 7. The composition ofclaim 1, wherein from about 12% to about 20% of the WTE BA aggregatefraction passes through a ⅜ inch sieve.
 8. The composition of claim 1,further comprising coal fly ash.
 9. The composition of claim 8, whereinthe Portland cement concrete comprises from about 2% to about 4% coalfly ash by weight.
 10. The composition of claim 1, further comprisingsilica fume.
 11. The composition of claim 10, wherein the Portlandcement concrete comprises from about 0.5% to about 1.5% of the silicafume by weight.
 12. The composition of claim 1, wherein the WTE BAaggregate fraction has been mixed with water to form an aqueoussuspension, wherein the aqueous suspension has a pH of about 8 to about11.
 13. The composition of claim 1, wherein the WTE BA aggregatefraction has reacted with CO₂ from a CO₂ source.
 14. The composition ofclaim 1, further comprising lime rock, sand, water, crushed stone,gravel, recycled concrete aggregate, recycled asphalt pavement, or anycombination thereof.
 15. An ash-amended pavement comprising thecomposition of claim
 1. 16. The ash-amended pavement of claim 15,wherein the ash-amended pavement leaches a lower amount of molybdenumrelative to an identical pavement that has not been ash-amended.
 17. Theash-amended pavement of claim 15, wherein the ash-amended pavement has acompressive strength of at least about 20 MPa.
 18. The ash-amendedpavement of claim 15, wherein the ash-amended pavement exhibits a wetlength change after 110 days of less than 0.1%.
 19. The ash-amendedpavement of claim 15, wherein the ash-amended pavement exhibits a drylength change after 110 days of less than 0.1%.
 20. The ash-amendedpavement of claim 15, wherein the ash-amended pavement comprises adifference in surface resistivity difference of less than or equal toabout 5 kΩ·cm compared to an identical pavement that has not beenash-amended.